Baker v. Carr
Baker v. Carr (369 U.S. 186 1962) was a case before the Supreme Court of the United States which decided that reapportionment issues (attempts to change the way voting districts are deliminated) do present a federal questions, thus enabling federal courts to intervene in and to decide reapportionment cases. The defendants unsuccessfully argued this is a political question and is not a federally justiciable question.
Plantiff Baker was a Republican who lived in Shelby County, Tennessee, the location of Memphis. His complaint was that even though the Tennessee state constitution required that legislative districts be redrawn every ten years according to the federal census to provide for districts of substansially equal population that this in fact had not been done since the census of 1900. By this point, his district in Shelby County had almost ten times as many residents as some of the rural districts. His arguement was that this discrepancy was causing him to fail to receive the "equal proctection under the laws" required by the Fourteenth Amendment.
Defendant Carr was Joe Carr in his position as Secretary of State for Tennessee. Carr was not the person who set the district lines -- the legislature had done that -- but was sued ex officio as the person who was ultimately responsible for the conduct of elections in the state and for the publication of district maps. The State of Tennessee argued that legislative districts were essentially political, not judicial questions, which is what past precedent had stated.
The finding for the plantiff had many ramifications. For one thing, the Court ruled that in states with bi-cameral legislatures that both houses had to be apportioned on the basis of "substansially equal" populations, voiding the provision of the Arizona constitution which had provided for two state senators from each county, and similar provisions elsewhere. (Critics of the ruling state that if this were a valid intrepretation, then the United States Constitution's own provision for two United States Senators from each state would then be "unconsitutional" as the fifty states have anything but "substansially equal populations".)
This precedent has allowed many issues to be litigated that were once decided by legislatures, notably the issue of minority-group representation and "minority-majority" districts, and the definition of "substansially equal population" and how much deviation between districts within a state is permissible.